Cytomegalovirus (CMV) has established persistent subclinical viral infections in the majority of the population. However, serious CMV-induced pathologies (blindness, hearing loss, mental retardation) occur in fetuses and newborns, as well as transplant recipients and acquired immunodeficiency syndrome (AIDS) patients (including retinitis and neuropathies), with immature or compromised immune systems. The ability of CMV to evade immune detection and elimination is facilitated by multiple proteins encoded in its genome that disrupt host processing and presentation of viral antigens, and interfere with chemokine and cytokine signaling.
The interleukin-10 (IL-10) signaling pathway is exploited by CMV, and many other viruses (e.g., human immunodeficiency virus (HIV), Hepatitis B and C) that establish persistent infections (Blackburn and Wherry, 2007; Rigopoulou et al., 2005). The main function of cellular IL-10 (cIL-10) is to protect the host from over-exuberant inflammatory responses by inhibiting the production of proinflammatory cytokines and chemokines, as well as major histocompatibility complex (MHC) and B7 on a variety of cell types (de Waal Malefyt et al., 1991a; de Waal Malefyt et al., 1991b). Human CMV (HCMV) and Rhesus CMV (RhCMV) encode functional IL-10 homologs (˜26% amino acid sequence identity to that of the cIL-10 proteins encoded by their human and rhesus hosts, respectively) that exhibit the same immunosuppressive activities of cellular IL-10 (Chang et al., 2004; Kotenko et al., 2000; Lockridge et al., 2000). Functional studies with HCMVIL-10 (cmvIL-10) have demonstrated that it prevents effective T-cell priming by inhibiting dendritic cell (DC) maturation and trafficking, as well as inhibiting interleukin-12 (IL-12), MHC, and co-stimulatory molecule production (Chang et al., 2004). The functions of cmvIL-10 appear to be critical to the life cycle of the virus since it is highly conserved in sequence amongst numerous culture-adapted strains and clinical isolates.
For biological activity, cIL-10 and cmvIL-10 must bind to the IL-10R1 and IL-10R2 receptor chains (Moore et al., 2001). Binding studies demonstrate that HuIL-10 and cmvIL-10 form equivalent high affinity (˜1 nM) interactions with the IL-10R1 chain and low affinity (˜μM) contacts with the IL-10R2 chain (Yoon et al., 2006). As a result, the IL-10/IL-10R1 interaction occurs first, followed by the assembly of the IL-10/IL-10R1/IL-10R2 ternary complex, which activates intracellular kinases (Jak1 and Tyk2) and transcription factors (STAT3) leading to IL-10 cellular responses (Moore et al., 2001).
The present invention provides the discovery that the cytomegalovirus IL-10 protein can be modified to have reduced functional activity while retaining immunogenicity. Thus, the present invention overcomes previous shortcomings in the art by providing such a modified cytomegalovirus IL-10 protein and biologically active fragments thereof, as well as nucleic acids encoding this protein and its fragments. These proteins, fragments and nucleic acids are used, for example, in methods of treating and preventing infection by cytomegalovirus.